function uncheckall() {
	var inputs = document.getElementsByTagName('input');
	for(var i = 0; i < inputs.length; i++) {
		inputs[i].checked = false;
	}
} //end of uncheckall()

function checkall() {
	var inputs = document.getElementsByTagName('input');
	for(var i = 0; i < inputs.length; i++) {
		inputs[i].checked = true;
	}
} //end of checkall()

function checksymmetry() {
	var inputs = document.getElementsByTagName('input');
	for(var i = 0; i < inputs.length; i++) {
		inputs[i].checked = !(inputs[i].checked);
	}
} //end of checksymmetry()